JP3395672B2 - Piezoelectric electroacoustic transducer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric electroacoustic transducer such as a piezoelectric buzzer, a speaker and a piezoelectric receiver.

[0002]

2. Description of the Related Art Conventionally, piezoelectric electroacoustic transducers have been widely used as piezoelectric receivers in mobile phones and the like. This type of piezoelectric electroacoustic transducer is disclosed in, for example, Japanese Patent Laid-Open No.
As described in JP-A-1079593 and JP-A-7-203590, a circular metal plate is attached to a single-sided electrode of a circular piezoelectric ceramic plate to form a unimorph type diaphragm, and a peripheral portion of the diaphragm is formed. Support in a circular case,
Generally, the case has a structure in which the opening is closed by a cover.

[0003]

However, in the case of the conventional piezoelectric-type electroacoustic transducer, a pair of front and back drive electrodes are provided with a piezoelectric ceramic plate in between so that one vibration plate has one resonance frequency. It has a formed structure. When such a diaphragm is incorporated in the case, one sound pressure peak is obtained at the resonance frequency, but the sound pressure sharply decreases before and after that frequency, so that the band becomes narrow at a predetermined sound pressure level.

In recent years, there has been a demand for a piezoelectric electroacoustic transducer capable of obtaining a predetermined sound pressure level in a wide band.
In order to meet such demands, there has been proposed a piezoelectric electroacoustic transducer in which a case that forms a resonance chamber is formed of a conductive thin plate, and a piezoelectric ceramic plate is adhered to two opposing surfaces of the case (actual flat panel). 6-29300). In this case, two disk-shaped piezoelectric ceramic plates are used, the lead wire is connected to the drive electrodes in common, the other lead wire is connected to the case, and the frequency signal is applied between these lead wires. By applying, the piezoelectric ceramic plates are expanded and contracted in opposite directions, and the expansion and contraction causes the entire case to flex and vibrate to generate sound.

In the case of this piezoelectric electroacoustic transducer, since the entire interior of the case serves as a resonance chamber, there is an advantage that a wide band can be achieved on the low frequency side. However, since the two piezoelectric ceramic plates resonate at the same frequency, a high sound pressure peak can be obtained at the resonance point, but a high sound pressure level cannot be obtained in a wide band. Moreover, since the entire circumference of the case, which is the diaphragm, is constrained, the vibration frequency becomes high, and there is a limit to widening the frequency band to the low frequency side. further,
Since the disk-shaped piezoelectric ceramic plate is used, the maximum displacement point is only the center point, and the displacement volume is small. This displacement volume serves as energy for moving air, and thus it is difficult to improve the acoustic conversion efficiency.

[0006] Therefore, an object of the present invention is to obtain a piezoelectric electroacoustic transducer having a low frequency and a wide band, and excellent acoustic conversion efficiency.

[0007]

In order to achieve the above object, the invention according to claim 1 is one rectangular metal plate,
A plurality of rectangular piezoelectric ceramic plates that are face-to-face joined to the metal plate and have different dimensions with drive electrodes formed on the surface, and the metal plate are housed, and a portion of the metal plate corresponding to the isthmus portion of the piezoelectric ceramic plate is formed. A case having a supporting portion for restraining and supporting, and a sealant for sealing the peripheral portion of the metal plate so as to be displaceable with respect to the case are provided, and a common frequency signal is provided between the drive electrodes and the metal plate. Provided is a piezoelectric electroacoustic transducer characterized in that the metal plate is flexibly vibrated by using a supporting portion as a fulcrum to obtain a sound pressure peak at a plurality of resonance frequencies.

When a plurality of piezoelectric ceramic plates are joined to a common metal plate and a common frequency signal is input between each drive electrode and the metal plate, the piezoelectric ceramic plate expands and contracts in the longitudinal direction,
In response to this, the metal plate causes bending vibration and produces a sound. At this time, the portion of the metal plate corresponding to the isthmus portion of the piezoelectric ceramic plate is constrained by the support portion of the case, and the peripheral portion of the metal plate is freely supported by the sealant, so the metal plate is fixed at the middle portion. It becomes a cantilevered support structure, and the vibration frequency can be reduced as compared with the case where both ends are supported or the periphery is fixed.
Metal plate part (vibration part) where each piezoelectric ceramic plate is joined
Vibrate simultaneously, but since the isthmus of each vibrating section is restrained by the supporting section, each vibrating section is separated and the vibration of one vibrating section is prevented from propagating to the other vibrating section via the metal plate. It can be prevented. Since each vibrating part is composed of drive electrodes having different dimensions, the resonant frequency of each vibrating part is different. By making these resonance frequencies close to each other, a piezoelectric electroacoustic transducer having a high sound pressure level in a wide band can be obtained.

The resonance frequency of each vibrating section depends on the shape of the piezoelectric ceramic plate. Since the piezoelectric ceramic plate has a rectangular shape, an arbitrary resonance frequency can be easily obtained by changing the length or width dimension. Also, with a conventional disc-shaped diaphragm, the maximum displacement point is only the center point, so the displacement volume is small, but in the case of a rectangular diaphragm, the maximum displacement point is the length or width direction. Since it exists along with, the displacement volume becomes large. Since this displacement volume serves as energy for moving air, the rectangular piezoelectric ceramic plate can improve the acoustic conversion efficiency as compared with the circular piezoelectric ceramic plate.

When the peripheral portion of the metal plate is sealed with respect to the case, a front air chamber and a rear air chamber which are acoustic spaces are formed on both sides of the metal plate. In particular, if the front air chamber having the sound output hole is made to be a common room, the volume of the front air chamber can be increased, so that the resonance frequency can be lowered. Therefore, in addition to the sound pressure peak due to the resonance frequency of each vibrating section, the sound pressure peak due to the resonance frequency appears on the lower frequency side than that, and a wider band can be realized.

To further increase the band, it is desirable to bond three or more piezoelectric ceramic plates to the metal plate. In this case, as in claim 2, a plurality of rectangular piezoelectric ceramic plates having different sizes are joined to the portion of the metal plate on at least one side of the supporting portion with the supporting portion interposed therebetween, and the rectangular ceramic ceramic plates corresponding to the isthmus portions of these piezoelectric ceramic plates are joined. It is desirable to form a slit in a direction orthogonal to the supporting portion at a portion of the metal plate to be formed, and to embed a sealant made of a rubber elastic material in the slit.

In this case, by providing a slit in the metal plate, it is possible to prevent vibration propagation between adjacent vibrating parts. When the slit is left open, the front and rear air chambers formed on both sides of the metal plate communicate with each other and sound cannot be produced, so the slit is sealed with a sealant such as a rubber elastic material that does not hinder vibration. By doing so, the front air chamber and the rear air chamber are shielded while preventing vibration propagation.

According to a third aspect of the present invention, a rectangular piezoelectric ceramic plate having a rectangular metal plate and two rectangular drive electrodes which are face-bonded to the metal plate and have different dimensions formed on the surface thereof. A case having a supporting portion for accommodating the metal plate and restraining and supporting a portion of the metal plate corresponding to the isthmus portion of the drive electrode; and a seal for sealing a peripheral portion of the metal plate displaceably with respect to the case. By providing a common frequency signal between each of the drive electrodes and the metal plate, the metal plate is flexibly vibrated with the supporting portion as a fulcrum, and a sound pressure peak is obtained at a plurality of resonance frequencies. A piezoelectric electroacoustic transducer characterized by the above is provided.

According to the present invention, a piezoelectric ceramic plate having a plurality of drive electrodes formed thereon is joined to one metal plate. The back side electrode of the piezoelectric ceramic plate may be one common electrode. Also in this case, similarly to the invention described in claim 1, by restraining and supporting the portion of the metal plate corresponding to the isthmus portion of the plurality of drive electrodes by the support portion of the case, the metal plate is cantilevered by the support portion. The vibration frequency can be lowered. Since each vibrating part is composed of drive electrodes having different dimensions, the resonant frequency of each vibrating part is different. By making these resonance frequencies close to each other, it is possible to obtain a piezoelectric electroacoustic transducer having a high sound pressure level in a wide band.

[0015]

1 to 6 show a piezoelectric receiver which is a first embodiment of a piezoelectric electroacoustic transducer according to the present invention. This piezoelectric receiver is generally a unimorph type diaphragm 1.
And a case 10 and a cover 20. The case 10 and the cover 20 constitute a case of the present invention.

The vibrating plate 1 includes a rectangular metal plate 2 and a metal plate 2.
It is composed of two rectangular piezoelectric ceramic plates 3 and 4 that are electrically and mechanically face-to-face bonded to each other. Metal plate 2
For example, a material having good conductivity and spring elasticity such as phosphor bronze or 42Ni is used. Metal plate 2 is 42Ni
In the case of, since the coefficient of thermal expansion is close to that of ceramic (PZT etc.), a more reliable one can be obtained. The piezoelectric ceramic plates 3 and 4 are made of piezoelectric ceramic such as PZT,
Electrodes 3a, 3b and electrodes 4a, 4b are formed on the front and back surfaces thereof (see FIG. 4), and the back surface electrodes 3b, 4b are face-bonded to the surface of the metal plate 2 with a conductive adhesive (not shown). Electrically connected. The back electrodes 3b and 4b may be omitted by directly bonding the back surfaces of the piezoelectric ceramic plates 3 and 4 to the metal plate 2 with a conductive adhesive.

Lengths x ₁ and x of the piezoelectric ceramic plates 3 and 4
₂ , at least one of the widths y ₁ and y ₂ and the thicknesses t ₁ and t ₂ is set to have different dimensions. for that reason,
The resonance frequencies of the two piezoelectric ceramic plates 3 and 4 are different from each other. In this embodiment, the settings are as follows. x ₁ > x ₂ y ₁ = y ₂ t ₁ = t ₂ By appropriately selecting the above dimensions, for example, the vibrating portion constituted by one piezoelectric ceramic plate 3 and the metal plate 2 has a resonance frequency of 2.880 kHz. And the other vibrating portion composed of the piezoelectric ceramic plate 4 and the metal plate 2 is 3.97.
It can be set to have a resonant frequency of 3 kHz.

The case 10 is integrally formed of resin, and two recesses 12 and 13 partitioned by a support wall (support portion) 11 are formed inside the case 10. Positioning protrusions 1 extending to the upper surface of the case 10 are provided at both ends of the support wall 11.
4 are formed and have a function of guiding both side edges of the diaphragm 1 by the inner surfaces of these protrusions 14. The diaphragm 1 is housed in the case 10 with a predetermined gap, and the gap between the peripheral edge of the diaphragm 1 and the inner surface of the case 10 is sealed with a sealant 15 having rubber elasticity such as silicone rubber. As a result, between the case 10 and the diaphragm 1, two rear air chambers 16,
17 (see FIG. 3) are formed. Since the sealant 15 has rubber elasticity, the peripheral edge of the diaphragm 1 is not constrained,
Allows free displacement. The intermediate portion 2a of the metal plate 2 corresponding to the isthmus portion of the piezoelectric ceramic plates 3 and 4 is fixed to the top surface of the support wall 11 with an adhesive 18. The adhesive 18 becomes a hard member after being hardened like an epoxy adhesive, and restrains and supports the intermediate portion 2a of the metal plate 2. By restraining and supporting the intermediate portion 2a of the metal plate 2 as described above, the metal plate 2 has a cantilever support structure in which the intermediate portion 2a is a fixed point, and the metal plate 2 can largely bend and vibrate. Further, by restraining the central portion 2a, the two vibrating portions are separated, and the vibration generated in one vibrating portion is prevented from reaching the other vibrating portion. In addition, braking holes 19 are formed on both side surfaces of the bottom of the case 10, and the rear air chambers 16, 17 are
Is open to the outside.

The cover 20 is also made of the same resin material as that of the case 10, and one sound emitting hole 21 is formed at the center of its ceiling. The peripheral portion of the cover 20 is fixed to the upper edge of the opening of the case 10 by a method such as adhesion or ultrasonic welding. Therefore, one front air chamber 22 (see FIG. 3) is formed between the cover 20 and the diaphragm 1.

A common lead wire 23 is connected to the surface electrodes (driving electrodes) 3a and 4a of the piezoelectric ceramic plates 3 and 4, and a lead wire 24 is connected to the metal plate 2, and these lead wires 23 and 24 are connected to each other. It is led out of the case 10. By applying a rectangular wave signal or a sine wave signal between the lead wires 23 and 24, it is possible to drive the two vibrating sections at the same time. In order to connect the surface electrodes 3a and 4a of the piezoelectric ceramic plates 3 and 4 and the metal plate 2 to the outside, lead terminals may be used instead of the lead wires 23 and 24.

The operation of the piezoelectric receiver having the above structure will be described below. When, for example, a rectangular wave signal is applied between the lead wires 23 and 24 and the frequency thereof is changed, the impedance changes as shown in FIG. 5, and the vibration composed of one piezoelectric ceramic plate 3 at a predetermined frequency. The part resonates, and the vibrating part composed of the other piezoelectric ceramic plate 4 resonates at another frequency. At this time, since the intermediate portion 2a of the metal plate 2 is fixed by the support wall 11 and the peripheral edge portion is displaceably supported,
In other words, it is in a cantilevered supporting state, and the metal plate 2 vibrates in the mode shown by the broken line in FIG. Therefore, the vibration frequency of each vibrating section can be made lower than in the case where both ends are supported or the periphery is fixed.

FIG. 6 shows changes in sound pressure with changes in frequency. As shown in FIG. 6, two sound pressure peaks appear, one sound pressure peak P ₁ is the resonance point of the vibrating portion formed by the piezoelectric ceramic plate 3, and the other sound pressure peak P ₂ is the piezoelectric ceramic plate 4. Is the resonance point of the vibrating section. Since the sound pressure level between the _two sound pressure peaks P ₁ and P ₂ is close to the two resonance frequencies, it is possible to ring in a wide band without causing a sudden decrease. In addition, in FIG. 6, a broken line indicates a sound pressure peak due to resonance of the front air chamber 22. The sound pressure peak P3 by the resonance for generating from the sound pressure peak P _1, P ₂ in the low frequency range, it is possible to further broaden as a whole.

FIG. 7 shows sound pressure characteristics A of a piezoelectric receiver using a vibration plate to which one rectangular piezoelectric ceramic plate is adhered, and 2
It is a comparison with a sound pressure characteristic B of a piezoelectric receiver using a vibration plate to which a rectangular piezoelectric ceramic plate is bonded. A rectangular wave having a peak-to-peak voltage of 3 V was used as the driving voltage. The dimension of the piezoelectric ceramic plate of characteristic A is 14 mm × 8.5 mm × 50 μm, and the dimension of the piezoelectric ceramic plate of characteristic B is 7.5 mm × 8.5 mm × 70
μm, and 5.5 mm × 8.5 mm × 70 μm. As the metal plates, square plates each having a size of 14 mm × 8.5 mm × 50 μm were used.

As is clear from FIG. 7, the frequency band at a sound pressure 6 dB lower than the sound pressure peak value is 0.959 kHz when one piezoelectric ceramic plate is used, while in FIG. When two piezoelectric ceramic plates (resonance frequencies of 2.880 kHz and 3.973 kHz, respectively) were used, the frequency was 2.010 kHz, and the band could be doubled. The sound pressure levels A and B are different because the measurement points are different and the thickness of the piezoelectric ceramic plate is different.

8 to 10 show a second embodiment of the present invention. In the vibration plate 30 of this embodiment, one rectangular piezoelectric ceramic plate 32 is face-bonded to an upper surface of a rectangular metal plate 31, and two rectangular shapes different in size are formed on the surface of the piezoelectric ceramic plate 32. Surface electrodes (driving electrodes) 33, 3 of
4 is formed. The piezoelectric ceramic plate 32
The back surface electrode 35 is formed on almost the entire surface.

The intermediate portion 31a of the metal plate 31 corresponding to the isthmus of the surface electrodes 33, 34 is the support wall 1 of the case 10.
It is restrained and supported by adhering it to the No. 1 with a hard adhesive 18. The peripheral edge of the metal plate 31 is sealed with an elastic sealant 15 on the inner surface of the case 10.

Also in the case of this embodiment, similarly to the first embodiment, the common lead wire 23 is connected to the surface electrodes 33 and 34, the lead wire 24 is also connected to the metal plate 31, and the space between these lead wires is connected. Apply a square wave signal or sine wave signal to. At this time, since the length dimensions x ₁ and x _{2 of} the surface electrodes 33 and 34 are different, they have two different resonance frequencies,
A wide range of sound pressure level can be obtained.

FIG. 11 shows a sound pressure characteristic A of a piezoelectric receiver using a vibrating plate to which one piezoelectric ceramic plate having one driving electrode is adhered, and one having two driving electrodes as shown in FIG. It is a comparison with a sound pressure characteristic C of a piezoelectric receiver using a vibration plate to which a rectangular piezoelectric ceramic plate is bonded.
The drive voltage is 3 from peak to peak.
A square wave of V was used. The dimension of the piezoelectric ceramic plate (electrode) of the characteristic A is 14 mm × 8.5 mm × 50 μm, and the dimension of the piezoelectric ceramic plate of the characteristic C is 14 mm × 8.
5mm × 70μm, electrode size is 7.5mm × 8.5mm
And 5.5 mm × 8.5 mm. 1 for both metal plates
A square plate of 4 mm × 8.5 mm × 50 μm was used.

As is apparent from FIG. 11, the frequency band at the sound pressure 6 dB lower than the sound pressure peak value is 0.959 kHz when one drive electrode is formed, whereas the frequency band of the two drive electrodes is two. Electrode (resonance frequency 3.72k each
Hz and 5.23 kHz), 2.475 kHz
z, and the band could be expanded about 2.5 times. The sound pressure levels A and C are different because the measurement points are different and the thickness of the piezoelectric ceramic plate is different.

12 to 14 show a third embodiment of the present invention. The vibrating plate 40 of this embodiment includes three rectangular piezoelectric ceramic plates 42, 4 having different dimensions on the upper surface of one metal plate 41.
3, 44 are face-to-face joined. The vibrating plate 40 is housed in the case 10 and includes piezoelectric ceramic plates 42 and 4
Intermediate part 41 of the metal plate 41 corresponding to the isthmus part with 3,44
a is supported by the support wall 11 of the case 10, and the hard adhesive 1
It is adhesively fixed by 8. An elastic sealant 15 is filled and sealed in the gap between the peripheral edge of the metal plate 41 and the inner surface of the case 10. A slit 41b is formed in a direction orthogonal to the support wall 11 at a portion of the metal plate 41 corresponding to a gap between the piezoelectric ceramic plates 43 and 44. The elastic sealant 15 is also filled in the slit 41b, and the slit 41b
The front air chamber 22 and the rear air chambers 16 and 17 are prevented from communicating with each other via the.

Also in the case of this embodiment, by applying a common signal (rectangular wave signal or sine wave signal) between the surface electrodes of the piezoelectric ceramic plates 42, 43 and 44 and the metal plate 41, each vibration is generated. The parts can be vibrated at the same time. At this time, the intermediate portion 41a of the metal plate 41 corresponding to the gap between the piezoelectric ceramic plates 42, 43 and 44 is fixed to the support wall 11, and the portion between the piezoelectric ceramic plates 43 and 44 is blocked by the slit 41b. Therefore, each vibrating part can vibrate independently. The vibration mode is the same as that shown by the broken line in FIG. Since the sound pressure peak is generated at the resonance point of each vibrating section, a high sound pressure level can be obtained in a wide band by bringing the resonance points close to each other. In particular, since the metal plate 41 has the intermediate portion 41a fixed and the periphery thereof can be freely displaced, it is a cantilever support structure, so to speak, and the vibration frequency can be lowered. As a result, low frequency and wide band can be realized.

15 to 17 show a fourth embodiment of the present invention. The vibrating plate 50 of this embodiment has four rectangular piezoelectric ceramic plates 52, 5 having different dimensions on the upper surface of one metal plate 51.
3, 54, 55 are face-to-face joined. The intermediate portion 51a of the metal plate 51 corresponding to the gap between the piezoelectric ceramic plates 52, 53 and 54, 55 is supported by the support wall 11 of the case 10 and is fixedly bonded by the hard adhesive 18. The elastic sealant 15 is filled and sealed in the gap between the peripheral edge of the metal plate 51 and the inner surface of the case 10. Slits 51b and 51c are formed in a direction orthogonal to the support wall 11 at the portions of the metal plate 51 corresponding to the isthmus portions of the piezoelectric ceramic plates 52 and 53 and the isthmus portions of 54 and 55. The elastic sealant 15 is also filled in the slits 51b and 51c, and through the slits 51b and 51c, the front air chamber 22 and the rear air chamber 16,
17 is prevented from communicating with.

Also in the case of this embodiment, by applying a common signal (rectangular wave signal or sine wave signal) between the surface electrodes of the respective piezoelectric ceramic plates 52 to 55 and the metal plate 51, the respective vibrating parts are separated. Can be vibrated at the same time. An intermediate portion 51a of the metal plate 51 located in the isthmus between the piezoelectric ceramic plates 52, 53 and 54, 55 is fixed to the support wall 11,
Since the portions between the piezoelectric ceramic plates 52 and 53 and between 54 and 55 are isolated by the slits 51b and 51c, each vibrating portion can vibrate independently. for that reason,
A high sound pressure level can be obtained in a wide band by generating a sound pressure peak at the resonance point of each vibrating section and bringing the resonance points close to each other. In particular, since the middle portion 51a of the metal plate 51 is fixed and the peripheral portion can freely vibrate, a low frequency can be realized.

The present invention is not limited to the above embodiments, but various modifications can be made without departing from the spirit of the present invention. For example, in the embodiments of FIGS. 15 to 17, individual piezoelectric ceramic plates are adhered to both sides of the middle part of the metal plate as a boundary, but as in the embodiments of FIGS. One piezoelectric ceramic plate may be adhered across the piezoelectric ceramic plate. Although the piezoelectric ceramic plate is attached to the front surface of the metal plate in the above embodiment, the piezoelectric ceramic plate may be attached to the back surface of the metal plate. That is, the metal plate may be arranged on the front air chamber side having the sound emission holes and the piezoelectric ceramic plate may be arranged on the rear air chamber side. Although the unimorph type diaphragm in which the piezoelectric ceramic plate is attached to one surface of the metal plate has been described in the above embodiment, a bimorph type diaphragm in which the piezoelectric ceramic plates are attached to both surfaces of the metal plate may be used. The piezoelectric electroacoustic transducer of the present invention can be applied not only to the piezoelectric receiver but also to a piezoelectric buzzer and a piezoelectric speaker.

[0035]

As is apparent from the above description, claim 1
According to the invention described in (1), a plurality of piezoelectric ceramic plates are joined to a common metal plate, the middle part of the metal plate is constrained and supported by the support part of the case, and both ends of the metal plate are displaceable by a sealant. Since it is sealed, the metal plate has a cantilevered support structure with the middle part as a fulcrum, which makes it possible to lower the vibration frequency compared to the both-ends support and fixed-periphery methods. The efficiency can be increased.

Further, since the size of the rectangular piezoelectric ceramic plate joined to both sides of the metal plate is changed, the resonance frequency of each diaphragm can be changed. Therefore, a plurality of sound pressure peaks can be easily obtained, and a wide band piezoelectric electroacoustic transducer can be obtained. Furthermore, since only one metal plate is stored in the case, the number of parts can be reduced, the cost can be reduced, and the case can be miniaturized as compared with the case where a plurality of metal plates are stored.

According to the third aspect of the invention, like the first aspect of the invention, by providing a plurality of drive electrodes on the piezoelectric ceramic plate, it is possible to individually vibrate each part, and to obtain a low-frequency wideband piezoelectric element. Type electro-acoustic transducer can be obtained.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a first embodiment of a piezoelectric electroacoustic transducer according to the present invention.

FIG. 2 is a plan view of the piezoelectric electroacoustic transducer shown in FIG. 1 with a cover removed.

FIG. 3 is a cross-sectional view of the piezoelectric electroacoustic transducer shown in FIG.

FIG. 4 is a plan view and a front view of a diaphragm used in the piezoelectric electroacoustic transducer shown in FIG.

5 is an impedance characteristic of the piezoelectric electroacoustic transducer shown in FIG.

6 is a sound pressure characteristic of the piezoelectric electroacoustic transducer shown in FIG.

7 is a comparison diagram of sound pressure characteristics of the piezoelectric electroacoustic transducer shown in FIG. 1 and a piezoelectric electroacoustic transducer using a single piezoelectric body.

FIG. 8 is a plan view showing a state where the cover of the second embodiment of the piezoelectric electroacoustic transducer is removed.

9 is a sectional view of the piezoelectric electroacoustic transducer shown in FIG.

FIG. 10 is a plan view and a front view of a diaphragm used in the piezoelectric electroacoustic transducer shown in FIG.

11 is a comparison diagram of sound pressure characteristics between the piezoelectric electroacoustic transducer shown in FIG. 8 and a piezoelectric electroacoustic transducer using a piezoelectric body having a single electrode.

FIG. 12 is a plan view showing a state where the cover of the third embodiment of the piezoelectric electroacoustic transducer is removed.

13 is a sectional view of the piezoelectric electroacoustic transducer shown in FIG.

14 is a plan view of a diaphragm used in the piezoelectric electroacoustic transducer shown in FIG.

FIG. 15 is a plan view of a piezoelectric electroacoustic transducer according to a fourth embodiment with a cover removed.

16 is a sectional view of the piezoelectric electroacoustic transducer shown in FIG.

17 is a plan view of a diaphragm used in the piezoelectric electroacoustic transducer shown in FIG.

[Explanation of symbols]

1 diaphragm 2 metal plate 3,4 Piezoelectric ceramic plate 3a, 4a Surface electrode (driving electrode) 10 cases 11 Support wall (support part) 15 Sealant 16,17 Rear air chamber 18 Adhesive 20 cover 22 Anterior chamber

Claims (3)

(57) [Claims] 1. A rectangular metal plate, a plurality of rectangular piezoelectric ceramic plates which are face-bonded to the metal plate and have driving electrodes formed on the surface, and which have different dimensions, and which house the metal plate.
A case having a supporting portion for restraining and supporting a portion of the metal plate corresponding to the isthmus portion of the piezoelectric ceramic plate; and a sealant for sealing the peripheral portion of the metal plate displaceably with respect to the case, By inputting a common frequency signal between each drive electrode and the metal plate, the metal plate is flexibly oscillated around the supporting portion as a fulcrum, and a sound pressure peak is obtained at a plurality of resonance frequencies. Piezoelectric electroacoustic transducer. 2. A plurality of rectangular piezoelectric ceramic plates having different sizes are joined to a portion of the metal plate on at least one side of the supporting portion with the supporting portion interposed therebetween, and the metal plate corresponding to the isthmus portion of these piezoelectric ceramic plates is formed. A slit is formed in the portion in a direction orthogonal to the supporting portion, and a sealant made of a rubber elastic material is embedded in the slit.
2. The piezoelectric electroacoustic transducer according to. 3. A single rectangular metal plate, a rectangular piezoelectric ceramic plate that is face-bonded to the metal plate and has two rectangular drive electrodes having different dimensions formed on the surface, and the metal plate. And a case having a supporting portion for restraining and supporting a portion of the metal plate corresponding to the isthmus portion of the drive electrode, and a sealant for sealing the peripheral portion of the metal plate so as to be displaceable with respect to the case,
By inputting a common frequency signal between each of the drive electrodes and the metal plate, the metal plate is flexibly vibrated with the supporting portion as a fulcrum, and a sound pressure peak is obtained at a plurality of resonance frequencies. Piezoelectric electroacoustic transducer.